Genes blamed for fickle female orgasm

Is this the ultimate excuse for poor performance in bed? "Sorry, darling," the man says, just before falling asleep. "It's your genes."

According to a study published this week, up to 45% of the differences between women in their ability to reach orgasm can be explained by their genes. Despite decades of surveys and conjecture about the role of culture, upbringing and biology in female sexual function, from Freud in 1905 to the Hite report in 1976, this is the first study of the role of a woman's genes.

Its findings suggest there is an underlying biological basis to a woman's ability to achieve orgasm. Whether that basis is anatomical, physiological or psychological remains uncertain, says Tim Spector of the twin research unit at St Thomas' Hospital in London, UK, who carried out the study.

"But it is saying that it is not purely cultural, or due to peer pressure, or to differences in upbringing or religion," he says. "There are wide differences between women and a lot of these differences are due to genes."

Mixed results

Spector's team asked more than 6000 female twins to fill out a confidential questionnaire about how often they achieved orgasm during intercourse and masturbation. They received 4037 complete replies, which included answers from 683 pairs of non-identical twins and 714 pairs of identical twins. The women's ages ranged from 19 to 83, and about 3% were lesbian or bisexual.

Only 14% of the women reported always experiencing orgasm during intercourse. Another 32% of the women reported that they were unable to achieve orgasm more than a quarter of the time, while 16% never achieved it at all. Comparing the results from identical and non-identical twins suggests that 34% of this variation in ability to orgasm during intercourse is genetic.

The idea behind twin studies is that pairs of twins grow up in similar environments. So if identical twins are more similar in some way than non-identical twins, then that similarity must be down to their identical genes rather than the environment.

Unsurprisingly, more women were able to achieve orgasm through masturbation, with 34% saying they could always do so. However, the figure for those who could never achieve it was only slightly lower, at 14%. The analysis suggests that 45% of this variation is genetic.

Men cleared

Spector says he was surprised by the similarity in the numbers of women unable to experience orgasm either through intercourse or masturbation. "With masturbation there are fewer external factors - i.e. men," he says. "So the higher heritability value for masturbation gives us a clearer picture of what's going on."

The discovery of a genetic basis for the ability of women to orgasm raises questions about its evolution. One theory is that it is a tool for mate selection, the idea being that males best able to bring females to orgasm are also the best males to help raise children. Another is that the female orgasm produces movements that increase sperm uptake, and therefore fertility.

But studies of other primates suggest otherwise. Female stump-tailed macaques have orgasms too - but mainly during female-female mountings, which hardly supports the fertility or mate-selection idea.

Bonobos engage in highly promiscuous sex and mutual masturbation, complete with orgasms, a practice that is thought to promote group cohesion. This supports yet another theory: that orgasm is important in bonding.

Accidental echo

But even if orgasm does play this role, it cannot be crucial in humans. The finding that many women cannot achieve orgasm because they do not have the genes for it shows that the ability to orgasm is not a trait for which there has been strong evolutionary selection, says Elisabeth Lloyd of Indiana University in Bloomington, author of The Case of the Female Orgasm. This supports her theory that as far as orgasms are concerned, women have been riding on the genetic coat-tails of male evolution, and that the female orgasm is merely an accidental echo of the male one, the equivalent of male nipples.

Lloyd says the findings also challenge the notion that the failure to achieve orgasm represents "female sexual dysfunction", an idea popular with companies keen to sell remedies for this so-called disorder. "What definition of 'normal' could possibly justify labelling a third of women as 'abnormal'?" she asks.

Even if struggling to achieve orgasm is nothing unusual, Spector says it might be possible to find ways to make it easier. Though hundreds of genes could be involved, "that doesn't mean we couldn't find the genes and pathways, if this was taken more seriously as a problem", he says.

If you would like to reuse any content from New Scientist, either in print or online, please contact the syndication department first for permission. New Scientist does not own rights to photos, but there are a variety of licensing options available for use of articles and graphics we own the copyright to.